1. Field of the Invention
This invention relates to a control apparatus for an internal combustion engine.
2. Description of the Related Art
When an internal combustion engine is operated at low speed such as idle speed, abrupt opening of a throttle valve of an air intake pipe may cause the knocking and starter pedal kickback (hereinafter called “kickback”) induced by reverse rotation of a crankshaft which occurs because air-fuel mixture burns before a piston passes the top dead center (TDC). Several techniques have been proposed for preventing such the kickback, etc., from occurring.
For example, it is known that, when a change amount of throttle opening is at or above a predetermined value, the ignition timing is retarded so as not to burn air-fuel mixture before a piston passes the TDC, as taught by Japanese Laid-Open Patent Application Nos. 2006-63971 ('971) and Hei 1(1996)-232169 ('169). Also, Japanese Laid-Open Patent Application No. 2006-274998 ('998) discloses a technique to detect engine speed of immediately before igniting, determine that the kickback likely occurs when the engine speed is decreased, and retard the ignition timing.
However, since the techniques in '971 and '169 are configured to retard the ignition timing when the change amount is at or above the predetermined value, the ignition timing is retarded even when the throttle valve is abruptly opened not in the intake stroke but in another stroke, i.e., even when the intake air is not increased and a compression load in the compression stroke is not increased. In this case, the engine output is unnecessarily decreased and it may adversely affect driving feel of the operator of the vehicle on which the engine is mounted.
Also, in the technique in '998 configured to retard the ignition timing to correspond to the engine speed of immediately before the ignition, the more the ignition timing is advanced relative to the TDC, the more it becomes difficult to accurately detect the decrease in the engine speed of immediately before reaching the TDC. Therefore, the kickback cannot be effectively prevented.
Further, in the case that the ignition is conducted when the forward rotation of a crankshaft is reversed, a reverse rotation load may affect the crankshaft, etc., and result in a damage of an engine body or the like. Japanese patent No. 2780257 discloses a technique to cope with this problem by disabling the ignition of the engine when the reverse of crankshaft rotation is detected.
In order to restart the engine after the ignition is disabled as above, the disabled condition has to be canceled and the cancellation is usually done at the time when the engine, precisely the crankshaft is stopped. A configuration to cancel the disabled condition after the elapse of a certain period of time after the ignition is disabled, is taught by Japanese Laid-Open Patent Application No. 2005-220866 ('866).
However, when, for example, the driver (operator) restarts the engine by manipulating a starter motor (or continuously manipulating a starter lever or kick starter pedal in the case of a motorcycle) before the engine, precisely the crankshaft is completely stopped, the engine can not be started because the ignition remains disabled. It is disadvantageous.
Even when the configuration set out in '866 is applied, the crankshaft is possibly still reversely rotated after the elapse of the certain period of time. The ignition after canceling the disabled condition under this circumstance may result in a damage of an engine body or the like, as described above.